Science You Can Use: You’re feeding your child a sugary and indigestible food. Good for you.

If I told you that I exclusively fed my babies a sugary and indigestible food for six months, would you think less of me? Wonder how they survived on a diet of Twinkies? Consider calling child welfare?

Well I did, and it turns out it was great for them in ways we’re only just starting to discover.

Two studies published in the last few weeks have looked at oligosaccharides and the gut bacteria of breastfed babies, and the findings are contributing to a new and powerful understanding of their role in our babies’ health.

Oligosaccharides are carbohydrates (sugars) that are present in large numbers in breastmilk – in a higher amount than fat, in fact. There are around 200 types of them in our milk. One mother’s milk may have anywhere from 23 to 130 of them, and they vary by the mother’s blood type, but as one review concluded, “the functional implications of this diversity are not known.”

Oligosaccharides were once thought to be useless because 90% of them end up in the baby’s diaper. They aren’t broken down in the baby’s stomach. Instead, they travel unfazed to the large intestine.

For some time we’ve known that they serve special functions there, blocking antigens from attaching to the surface of the baby’s intestines, and maintaining a pH that is inhospitable to bad bacteria. They’re known to be effective at blocking pneumococcus, a particularly “sticky” antigen, and some theorize that this blocking action may even explain why some HIV positive mothers don’t transmit the virus to their children through breastmilk. Research dating a century back suggested that they serve as a food source for beneficial bacteria – bacteria we now call probiotics (now interrupting your TV shows as Activia yogurt).

But it turns out that this understanding is probably just the tip of the iceberg.

Two new studies are demonstrating the power of oligosaccharides and the function of a healthy “microbiome” in a baby’s gut. One study, from the University of Illinois, found:

Human milk oligosaccharides, or HMO, produce short-chain fatty acids that feed a beneficial microbial population in the infant gut. Not only that, the bacterial composition adjusts as the baby grows older and his or her needs change.

For the first time, scientists have shown that a complex mixture of HMO and a single HMO component produce patterns of short-chain fatty acids that change as the infant gets older.

A healthy microbiome has both short- and long-term effects on an infant’s health. In the short term, beneficial bacteria protect the infant from infection by harmful bacteria. In the long term, beneficial bacteria strengthen the immune system so that it can fend off chronic health problems like food allergies and asthma, she says.

The results show that three-month-old babies that had been fed only breast milk had a wider range of bacteria in their guts than babies that were fed only formula. The researchers also found a link between the bacteria in the babies’ guts and changes in the expression of genes involved in their immune systems.

…the researchers also found increased activity of immunity genes known to be involved in defending the gut tissue against foreign invaders, said study researcher Robert Chapkin, a professor of Nutrition, Biochemistry and Biophysicsat the Texas A&M University.

“Our findings suggest that human milk promotes the beneficial crosstalk between the immune system and microbe population in the gut, and maintains intestinal stability,” Chapkin said.

To summarize, not only do oligosaccharides block bad bacteria, feed good bacteria, and make the weather inhospitable to bad bacteria in the baby’s gut, they also change to meet the needs of growing babies. Breastfed babies guts have a more diverse community of bacteria, and this may change the way the baby’s immune system functions by altering the way way its genes act. (Altering gene expression is a particularly potent crime fighting power because changes to our “epigenome” may actually pass from one generation to the next.)

You may have heard that some formulas now include prebiotics, but as one comprehensive review of oligosaccharides concluded, “These infant formula oligosaccharides are not naturally present in human milk and are structurally different from the oligosaccharides naturally occurring in human milk (HMOs). Most of the effects attributed to HMOs appear to be highly structure dependent. Therefore, infant-formula oligosaccharides may have different effects than HMOs.”

Human milk evolved over thousands of years to provide just the right balance of nutrition and protection for infants. So it was always silly of us to think that the complex sugars in breastmilk were “junk food.” The hard, but intriguing work is figuring out exactly how they work.